5 Structure of the Skeletal SystemAxialAppendicularSkeletal SystemWithout the skeletal system you would be a shapeless bag of soft organs collapsed on the floor. You would be helpless. You would not be able to perform movements such as walking or grasping. The slightest bump to your head or chest could damage the brain or heart. It would even be impossible to chew food. There are 206 bones in the human body.Axial Skeleton: supports head neck thorax; protects brain, spinal cord, organsskullvertebraerib cage2. Appendicular SkeletonA. Pectoral Girdle: anchors upper limbsWeak attachment at clavicle/sternum but flexible – FREEDOM OF MOVEMENTB. Upper LimbC. Pelvic Girdle: Attaches lower limbsVery strong attachment at sacrum – BALANCE, WEIGHT TRANSMISSIOND. Lower Limb

6 The Structure of Bone: Compact Bone & Spongy BoneForms outer part of bonesBears weightSpongy boneMade of trabeculae (latticework)Located inside bonesReduces weight of boneC. Bone Tissue TypesThere are two types of bone tissue based on how cells/matrix are arranged:Compact - one that looks more dense, more compact. It makes the outer part of bones and forms the shaft of long bones. It BEARS WEIGHT.Spongy - one that looks like swiss cheese or like a sponge. The cells and matrix are laid down irregularly. The lattice work is called trabeculae. Spongy bone is located inside bones. (knobs, flat) It REDUCES THE WEIGHT OF BONE. Also, can change arrangement of trabeculae in response to weight.

8 4 Types of Bone Shapes Long bones Short bones Flat bonesIrregular bonesLong – like the femur. Usually have shaft with two “heads”. Made up mostly of compact.Short – more cube-shaped. Made up mostly of spongy boneFlat bone – skull, ribs. Made up of two thin layers of compact bone with spongy bone inbetween.Irregular bone – vertebrae, hips.

9 Anatomy of a Long Bone epiphysis (head) diaphysis (shaft) epiphysisLong bones have two heads – epiphyses, and a shaft – diaphysis.The epiphyses are mostly spongy bone. RED MARROW is found here.The diaphysis is hollow. The outside is compact bone. Yellow marrow inside.MembranesBoth external and internal bone surfaces are covered with membranes. The membranes cover and protect the surface of the bones. They have blood and nerve tissue. The periosteum (outer membrane) is subject to a lot of pulling: it is connected to tendons (b – m) and ligaments (b – b).epiphysis

11 Bone is a Living Tissue!!!It is made of living cells embedded in a non-living matrix.It grows, remodels and repairs.It responds to hormonal stimulation.

12 Made of Living Cells Osteon Lacunae CanniculiA. Made of living cells embedded in a non-living matrix.Note the osteon: mature bone cells arranged in rings around a central canal. These canals have blood vessels and nerves.The cells are surrounded by a hard substance – the matrix – here composed mostly of calcium salts. The “hard stuff”.Since the cells lie far apart from each other, connective tissue. Cells exchange information with each other via canniculi.

13 Matrix minerals proteins **strength and flexibility The MatrixThis is the extracellular space.* filled will mineral salts (1* Ca) – 2/3 of matrix, these salts give bone its hardness – different from other tissue.* also 20% protein (rest is water)- bone is hard, but flexible: it would be brittle if just minerals, so it is embedded with proteins & collagen fibers.Bone soaked in acid – leaches salt out (rubbery)Bone baked in oven – destroys protein (brittle)

14 Bone Cells Types Osteoblast – bone builders – form matrixOsteocyte – bone maintainers – maintain matrixOsteoclast – bone dissolvers – destroy matrixBone Cells – form and maintain the matrix You can see why the matrix is important – this is what we think of when we think of bone. So what role do the cells play in bone?Osteoblasts – “bone builders” – secrete the matrixOsteocytes – “bone maintainers” - embedded in and maintain matrix (does not secrete)Osteoclasts – “bone dissolvers” – destroy the matrix

15 Bone is a Living Tissue!!!It is made of living cells embedded in a non-living matrix.It grows, remodels and repairs.It responds to hormonal stimulation.

22 Bone is a Living Tissue!It is made of living cells embedded in a non-living matrix.It grows, remodels and repairs.It responds to hormonal stimulation.Hormones regulate bone growth. Growth effected by various hormones - GH during childhood – testosterone and estrogen surges at puberty – which cause an incredible surge in cell division at growth plates. In adulthood, growth plates replaced by bone.Bones also respond to PTH (parathyroid hormone). When blood calcium levels are too low, PTH activates osteoclasts to break down bone (releasing calcium to blood stream).